Parabolic solar collectors are among the best known types of solar collectors for concentrating solar radiation to a focal point. Parabolic collectors are also used for concentrating electromagnetic rays to a spot and used onboard satellites as well as in ground stations for concentrating radiation to a sensor. Database indicates there are numerous patents related to parabolic collectors.
Literature survey indicated several documents that summarize state of the art in parabolic solar collectors. One of the documents is authored by H. E. Imadojemu and published in Vol. 36, No. 4 issue in pages pp. 225-237, 1995 of Energy Conversion Management Journal. This document is titled “Concentrating Parabolic Collectors: a Patent Survey”. Another article published is by S. Kalogirou and published in the Journal of Recent Patents on Engineering in 2007, issue #1, pages 23-33. The publication by Kalogirou is titled as “Recent Patents in Solar Energy Collectors and Applications”. The state of the art in solar collectors is summarized in these articles.
Parabolic solar collectors are type of mirrors which have parabolic shape and installed facing towards sun. The solar rays coming from the mirror are focused to a specific spot where an energy absorber or a secondary mirror is placed. These types of solar collectors are known as “SRTA” which stands for Stationary Reflector/Tracking Absorber configuration. In this particular configuration the solar concentrator is stationary, but due to changing position of sun, the point where the solar radiation is focused changes continuously in a well defined path. This is where the tracking absorber is used; by placing the absorber always in the focal point of the solar collector, it is possible to receive energy no matter what time of the day is.
The main problem with parabolic type SRTA's is the construction of the parabolic mirror. Although small size parabolic mirrors can be cast efficiently using carefully designed molds, making oversized parabolic mirrors has been difficult and challenging. There have been patents toward methods of making parabolic mirrors such as U.S. Pat. No. 4,124,277 “Parabolic Mirror Construction” and U.S. Pat. No. 4,860,023, “Parabolic Reflector Antennas and Method of Making Same”. Another recent patent application; US 2010/010-8057A1, “Inflatable Solar Concentrator Baldwin Method and Apparatus” are among different attempts for making parabolic solar collectors.
The invention declares a method of making stationary parabolic concave mirror and an apparatus specifically designed for this purpose. The primary goal of this invention is to make large scale parabolic mirrors quickly and accurately. One of the most difficult aspects of parabolic mirror construction is formation of the specific parabolic shape accurately. The invention teaches a practical method of determining the exact location and height of the structural elements of the parabolic mirror so that the mirror constructed over the structural elements end up having the required parabolic concave shape.
U.S. Pat. No. 3,998,206 to Jahn discloses a parabolic mirror made from numerous prefabricated mirror tiles arranged on a rib-like structure for forming a parabolic mirror.
Another U.S. Pat. No. 4,002,032 to Bash discloses a solar heated turbine where the solar rays are focused to a target using a parabolic dish like structure.
Another U.S. Pat. No. 4,170,985 to Authier discloses a stationary solar collector and high concentration boiler arrangement for converting focused solar heat to heat transfer liquid.
Yet another U.S. Pat. No. 5,680,145 to Thomson et. Al. discloses a lightweight structure for building parabolic reflectors for solar or electromagnetic reflection purposes.
Japan patent JP 59-097460 issued to Horigome discloses a stationary reflector embedded in the ground and a fiber optic target arrangement which can be moved to focal point of the parabolic reflector to collect the solar rays and conducted to a stationary energy conversion device.
Although all these inventions stated above are somehow related to parabolic reflectors and have a merit on their own, the invention declared in this application discloses a different method for constructing parabolic reflectors.